取代1-氯蒽醌中分子内卤键的电子密度拓扑分析

运用量子化学密度泛函B3LYP方法,在6-311＋＋G（d,p）基组水平上对邻位和间位取代1-氯葸醌的分子内卤键进行了研究．用电子定域函数和“分子中的原子,,理论对分子内卤键的性质进行了电子密度拓扑分析．通过对计算得到的密度矩阵进行σ-π兀分离,得到了π-键的键径和分子图,并讨论了。电荷密度和兀电荷密度对卤键的影响．结果表明,键鞍点和环鞍点处的电子密度拓扑性质均可作为衡量分子内卤键强度的量度．键鞍点和环鞍点处的电荷密度P越大,键鞍点与环鞍点的距离越大,卤键强度越大．除σ电荷密度外,π电荷密度对分子内卤键的性质也有明显影响．     

Chromo-chemodosimetric detection for Fe2+ by Fenton reagent-induced chromophore-decolorizing of halogenated phenolsulfonphthalein derivatives

A commercially-available sulfonphthalein derivative was demonstrated to be a chemodosimeter for Fe²⁺ and its sensing behavior was further investigated by UV-vis spectroscopy in aqueous media under the optimum conditions. In the presence of chlorophenol red (CPR) and H₂O₂, the absorption maximum at 435 nm decreased upon addition of Fe²⁺, resulting in a significant color change of the CPR solution from yellow to colorless. The chemosensor system did not show significant responses to a series of other metal ions including Al³⁺, Zn²⁺, Cd²⁺, Hg²⁺, Mn²⁺, Co²⁺, Fe³⁺, Ni²⁺, Cu²⁺, La³⁺, Ce⁴⁺, Th⁴⁺, Pd²⁺, Pb²⁺, Sb³⁺, Cr³⁺, Au³⁺, Ag⁺, Nd³⁺, Sm³⁺, alkali and alkaline earth metal cations, allowing for highly selective naked-eye detection of Fe²⁺. Quantitative analysis was carried out kinetically for practicable the Fe²⁺ assay when either fixed time method or the initial rate method was applied. When the detecting time was set, the decrease of absorbance signal was linear with Fe²⁺ concentration in the range of 0 to 7.50 × 10^?5 mol L^?1 and the regression equation was ΔA = 0.00759 + 0.00593C _Fe with a correlation coefficient r = 0.9953. The chemodosimetric system has employed an irreversible Fenton reagent-promoted oxidation of the CPR free chromophore and the hydroxyl radicals were generated in the presence of both Fe²⁺ and hydrogen peroxide. The mechanistic interpretation of the signaling process was partially confirmed by the radical scavenging experiment and the FT-IR analysis of the intermediates formed at different reaction periods.     

Enantioselective separation and dissipation of pydiflumetofen enantiomers in grape and soil by supercritical fluid chromatography–tandem mass spectrometry

Pydiflumetofen is registered in many countries and is widely used in crop production in the racemate form. However, the environmental behavior of the enantiomers has not been studied. An effective and sensitive chiral analytical method was first established for analyzing the pydiflumetofen enantiomers by supercritical fluid chromatography with tandem triple quadrupole mass spectrometry. The enantiomers could be separated and detected using the Chiralcel OD‐3 column in less than 3 min. The separation conditions were as follows: mobile phase, CO₂/methanol (80:20); flow rate, 1.0 mL/min; column temperature, 30°C, auto back‐pressure regulator pressure, 2000 psi with modified quick, easy, cheap, effective, rugged, and safe sample treatment method. The average recoveries of analytes from both matrices at three spiking levels were in the range of 84.1–103.0%. The limit of quantitation for each enantiomer was 0.005 mg/kg with a baseline resolution of approximately 1.64. The method was applied to monitor the enantioselective dissipation of pydiflumetofen in grape and soil. In grapes, (?)‐pydiflumetofen was degraded more rapidly than (+)‐pydiflumetofen. In soil, (+)‐pydiflumetofen was preferentially degraded. The data provided useful references for the risk assessment and rational use of pydiflumetofen in agriculture.     

Quantification of flupirtine maleate polymorphs using X-ray powder diffraction

Flupirtine maleate,a pharmaceutical compound for treating psychotic disease in clinics,has seven polymorphs.Form A,with better crystal stability and bioavailability,has been widely used as the pharmaceutical crystal form.Unfortunately,it is usually found in a polymorphic mixture with form B.In this study,pure crystal forms of A and B were prepared and characterized by X-ray powder diffraction (XRPD),Fourier transform infrared spectroscopy (FT-IR) and thermal analysis.An XRPD-based method for the quantitative determination of the amount of the flupirtine maleate polymorphs form A and form B was also established through a systematic optimization of instrumental parameters.The results of the analytical methodology validation showed that the XPRD method had a broad quantitative range of 0-100%(w/w),good linear relationship,with R²=0.999,excellent repeatability and precision and low limits of detection (LoD) of 0.15%(w/w) and quantification (LoQ) of 0.5%(w/w).The results also showed that the single-peak method was not as good as the whole pattern in reducing the influence of the preferred orientation,but this can be compensated for by a systematic optimization of instrumental parameters and validating the analytical methodology to reduce errors and obtain a good,repeatable,sensitive,and accurate method.This XRPD method can be used to analyze mixtures of flupirtine maleate polymorphs (forms A and B) quantitatively and control the quality of the bulk drug.     

BEM for simulation of a 2D elastic body with randomly distributed circular inclusions

Based on our 2D BEM software THBEM2 which can be applied to the simulation of an elastic body with randomly distributed identical circular holes, a scheme of BEM for the simulation of elastic bodies with randomly distributed circular inclusions is proposed. The numerical examples given show that the boundary element method is more accurate and more effective than the finite element method for such a problem. The scheme presented can also be successfully used to estimate the effective elastic properties of composite materials. Project supported by the National Natural Science Foundation of China (No. 19772025).     

Iron Catalyzed Isomerization of α-Alkyl Styrenes to Access Trisubstituted Alkenes

Stereoselective isomerization of α-alkyl styrenes is accomplished using a new iron catalyst supported by phosphine-pyridine-oxazoline (PPO) ligand.The protocol ...     

Production of Atosiban’s Key Intermediate Pentapeptide: Synthetic Approaches to the Development of a Peptide Synthesis with Less Racemization and Simplifier Purification Process

The key intermediate NH₂-Ile-Thr(Bzl)-Asn-Cys(Bzl)-Pro-COOH of Atosiban was prepared from N-Boc-S-Bzl-cysteine by the stepwise lengthening of the chain according to the repetitive N,O-bis(trimethylsilyl)acetamide/N-hydroxysuccinimide ester (BSA/NHS) strategy. This synthetic route required no chromatography purification and can be readily performed, yielding a highly pure pentapeptide compound.     

Graphene-Oxide-Based Fluoro- and Chromo-Genic Materials and Their Applications

Composite materials and their applications constitute a hot field of research nowadays due to the fact that they comprise a combination of the unique properties of each component of which they consist. Very often, they exhibit better performance and properties compared to their combined building blocks. Graphene oxide (GO), as the most widely used derivative of graphene, has attracted widespread attention because of its excellent properties. Abundant oxygen-containing functional groups on GO can provide various reactive sites for chemical modification or functionalization of GO, which in turn can be used to develop novel GO-based composites. This review outlines the most recent advances in the field of novel dyes and pigments encompassing GO as a key ingredient or as an important cofactor. The interactions of graphene with other materials/compounds are highlighted. The special structure and unique properties of GO have a great effect on the performance of fabricated hybrid dyes and pigments by enhancing the color performance of dyes, the anticorrosion properties of pigments, the viscosity and rheology of inks, etc., which further expands the applications of dyes and pigments in dyeing, optical elements, solar-thermal energy storage, sensing, coatings, and microelectronics devices. Finally, challenges in the current development as well as the future prospects of GO-based dyes and pigments are also discussed. This review provides a reference for the further exploration of novel dyes and pigments.     

Levitation performance of the magnetized bulk high-Tc superconducting magnet with different trapped fields

To a high-T_c superconducting (HTS) maglev system which needs large levitation force density, the magnetized bulk high-T_c superconductor (HTSC) magnet is a good candidate because it can supply additional repulsive or attractive force above a permanent magnet guideway (PMG). Because the induced supercurrent within a magnetized bulk HTSC is the key parameter for the levitation performance, and it is sensitive to the magnetizing process and field, so the magnetized bulk HTSC magnets with different magnetizing processes had various levitation performances, not only the force magnitude, but also its force relaxation characteristics. Furthermore, the distribution and configuration of the induced supercurrent are also important factor to decide the levitation performance, especially the force relaxation characteristics. This article experimentally investigates the influences of different magnetizing processes and trapped fields on the levitation performance of a magnetized bulk HTSC magnet with smaller size than the magnetic inter-pole distance of PMG, and the obtained results are qualitatively analyzed by the Critical State Model. The test results and analyses of this article are useful for the suitable choice and optimal design of magnetized bulk HTSC magnets.     

Inversion of two-band superconductivity at the critical electron doping of (Mg, Al)B2

Electron energy-loss spectroscopy (EELS) was combined with heat capacity measurements to probe changes of electronic structure and superconductivity in Mg(1-x)Al(x)B(2). A simultaneous decrease of EELS intensity from sigma-band hole states and the magnitude of the sigma gap was observed with increasing x, thus verifying that band filling results in the loss of strong superconductivity. These quantities extrapolated to zero at x approximately 0.33 as inferred from the unit cell volume. However, superconductivity was not quenched completely, but persisted with T(c) < 7 K up to about x approximately 55. Only the pi band had detectable density of states for 0.33 < or =x < or = 0.55, implying an inversion of the two-band hierarchy of MgB(2) in that regime. Since pi-band superconductivity is active in other materials such as intercalated graphite, implications for new materials with high T(c) are discussed.